In order to generate a so-called parallax image (also referred to as a three-dimensional image or a 3D image) that supports stereoscopic vision (three-dimensional vision), it is necessary to prepare images from different viewpoints, i.e., a left eye image and a right eye image. More specifically, images having parallax are generated as a left eye image and a right eye image, and control is performed such that the left eye image is observed with only the left eye of an observer (user) and the right eye image is observed with only the right eye of the observer (user), so that the observer can feel stereoscopic feeling.
Configurations for allowing a user to observe each image with only one of the eyes include various methods. Examples include a passive-glasses method for separating images observed with the right and left eyes from each other using polarization filters and color filters and an active-glasses method for time-divisionally separating images to right and left images using a liquid crystal shutter. In general, stereoscopic images can be observed by observing images with such special three-dimensional vision glasses.
As described above, various methods have been suggested in the past as methods for achieving three-dimensional vision by presenting images having parallax.
However, when the parallax range is too narrow, i.e., when a width between a subject seen in proximity and a subject seen at a distance is too narrow, there is a problem in that a user is unable to sufficiently feel stereoscopic feeling. On the other hand, it is reported that there are some observers who feel tired or sickness when they continue to observe three-dimensional images with large parallax ranges for a long period of time. As a method for solving such problem, a method for controlling the amount of parallax has been suggested in order to give appropriate stereoscopic feeling.
For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 07-167633) discloses a method for detecting a retinal image difference (disparity) corresponding to parallax from right and left images (a left eye image and a right eye image) constituting a three-dimensional image and adjusting the parallax by horizontally shifting the right and left images on the basis of the detected retinal image difference (disparity) information. In other words, this method disclosed in Patent Document 1 is an image conversion method for setting a parallax range that can be comfortably seen by an observer, by horizontally shifting the entire image using an average value of disparities.
It should be noted that the disparity is a retinal image difference or a value corresponding to a distance, on a display unit, between a subject in the left eye image and the same subject in the right eye image, and the larger the disparity is, the larger the parallax is.
This method disclosed in Patent Document 1 is an image conversion method for setting a parallax range that can be comfortably seen by an observer, by horizontally shifting the entire image using an average value of disparities.
In this configuration disclosed in Patent Document 1, the amount of horizontal shift is determined using an average value of disparities, and there is an advantage in that conversion can be performed with less amount of processing. In this configuration disclosed in Patent Document 1, however, the entire right and left images are horizontally shifted, and there is a problem in that the dynamic range of parallax (difference in depth between the closest subject and the farthest subject) cannot be controlled.
On the other hand, Non-patent Document 1 (“Stereoscopic image generation based on depth image for 3D TV”, L. Zhang and W. J. Tam, IEEE Trans. On Broadcasting, Vol. 51, No. 2, June 2005) discloses a method for generating a disparity map describing disparity corresponding to each pixel of images (displacement between a left image and a right image) from the right and left images and recovering images for different viewpoints, using the disparity map and the original images.
With this method disclosed in Non-patent Document 1, an image from a new viewpoint can be generated, and images can be generated in which the dynamic range of parallax of the stereo image are also controlled. In this method described in Non-patent Document 1, however, it is essential to generate the disparity map describing disparity (image difference) for each pixel of images, and this increases the processing cost, and there is a problem in that it is difficult to reduce the size of the circuit. Moreover, since the quality of the generated images depends on the accuracy of the disparity map, it is required to generate the disparity map with a high resolution and a high degree of accuracy. It is difficult to generate such disparity map with a high degree of accuracy, which becomes a factor for increasing the size of the circuit.